Retaining walls are used in various landscaping projects and are available in a wide variety of styles. Numerous methods and materials exist for the construction of retaining walls. Such methods include the use of natural stone, poured concrete, precast panels, masonry, and landscape timbers or railroad ties.
In recent years, segmental concrete retaining wall units, which are dry stacked (i.e., built without the use of mortar), have become widely accepted in the construction of retaining walls. An example of such a unit is described in U.S. Pat. No. Re 34,314, which issued to Forsberg (Forsberg '314). Such retaining wall units have gained popularity because they are mass produced and, consequently, relatively inexpensive. They are structurally sound, easy and relatively inexpensive to install, and couple the durability of concrete with the attractiveness of various architectural finishes. The retaining wall system described in Forsberg '314 has been particularly successful because of its use of a block design that includes, among other design elements, a unique pinning system that interlocks and aligns the retaining wall units, thereby providing structural strength and allowing efficient installation. This system is advantageous in the construction of larger walls, when combined with the use of geogrids hooked over the pins, as described in U.S. Pat. No. 4,914,876 to Forsberg ('876).
Another important feature of retaining wall blocks is the appearance of the block. The look of weathered natural stone is very appealing for retaining walls. There are several methods in the art to produce concrete retaining wall blocks having an appearance that to varying degrees mimics the look of natural stone. One well known method is to split the block during the manufacturing process so that the front face of the block has a fractured concrete surface that looks like a natural split rock. This is done by forming a slab in a mold and providing one or more grooves in the slab to function as one or more splitting planes. The slab is then split apart to form two or more blocks. Another method is wherein blocks are individually formed in a mold and the surfaces are textured by removal of the mold. Additional machine texturing processes can then be applied.
Creating a random, or ashlar, pattern in the face of a retaining wall is highly desirable. This gives the appearance of a mortared or dry-stacked natural stone wall, which is a traditional and well accepted look. Some current wall blocks are intended to create an ashlar pattern. However, the creation of a truly random appearance requires the production of multiple block shapes for use in a single retaining wall. This is inefficient from a production standpoint because this requires multiple molds and more kinds of blocks to inventory. If only one face of the block is intended to be the front face, then the block system will suffer a trade-off between having enough face sizes to create a random, natural appearance and the cost and inefficiency of using multiple molds and creating multiple inventory items.
Because of the natural variation in size of the stones used in stone retaining walls, the wall surface has variations in width from stone to stone. A system capable of duplicating this effect is described in U.S. Pat. No. 6,149,352 (MacDonald), hereby incorporated herein by reference in its entirety. This system uses blocks of different widths and a connection system comprising a channel on each block and multiple pin receiving cavities to align the blocks. Thus this system can be used to produce a wall having random variations in face width and high structural integrity of the wall structure.
However, problems still remain in the field of retaining walls. Easy-to-use methods and systems that permit strengthening the wall, as well as tying in reinforcing geogrids into the earth behind a retaining wall, are continually sought.
It would be desirable to have a system of blocks for constructing a retaining wall that combines the ability to improve the reinforcement of the wall with the ease of installation of modern segmental retaining walls, while still providing for an attractive appearance of a natural stone wall. The block system should allow the construction of freestanding walls as well as curved walls and walls with 90 degree corners.